Sudden Cardiac Arrest (SCA) is one of the leading causes of death in the United States. Each year, it is estimated that over 450,000 Americans die from SCA. SCA occurs when the heart stops beating normally and is no longer able to effectively pump oxygenated blood to the brain and other vital organs. When a person experiences SCA, delivery of treatment as quickly as possible is critical as death can occur within minutes. Currently, the only known effective treatment to halt SCA is prompt external or internal defibrillation.
External defibrillation is a treatment process in which an electrical waveform, hereafter referred to as an electrical defibrillation pulse, is applied to the cardiac muscle resulting in the cessation of rapid uncoordinated contractions of the heart. Following external defibrillation, the heart is restored to its normal beating state. External defibrillation treatment is commonly administered with an automated external defibrillator that includes heart rhythm sensors, current generating circuitry and electrode pads for delivering the electrical defibrillation pulse. Automated external defibrillators are available in a variety of configurations including varieties frequently seen in hospitals or on television as well as the smaller, more portable models frequently found in airplanes, shopping malls, stadiums and nursing homes.
Using the heart rhythm sensors, the automated external defibrillator is able to determine whether a person is actually suffering from SCA and if electrical defibrillation is required. If the sensors determine that electrical defibrillation is necessary, the current generating circuitry discharges, delivering the electrical defibrillation pulse through the electrode pads which are positioned over the chest area of the person.
Due to the size and density of the chest cavity, it is estimated that only 4% of the current delivered by the automated external defibrillator actually reaches the heart. This ability of the chest cavity to impede the flow of electrical current is known as transthoracic impedance. Transthoracic impedance is created by the combination of air present in the lungs, fat tissue, muscle tissue, breast tissue, skin, bones and body hair. Due to this transthoracic impedance, automated external defibrillators are typically designed to deliver electrical defibrillation pulses having energy levels of 350–400 Joules such that the heart actually experiences energy levels of between 10–50 Joules.
While the current designs of automated external defibrillators perform excellently with respect to treating SCA, it would be desirable to have an automated external defibrillator design which would eliminate the tremendous current losses inflicted by transthoracic impedance. Such a design would result in an automated external defibrillator that is both more efficient and consequently less expensive to manufacture.